Geophysical properties, geochronologic, and geochemical data of sediment cores collected from San Pablo Bay, California, October 17-20, 2016

CORE COLLECTION: Sediment cores were collected with a Rossfelder P-5 vibracorer. Cores were cut into 150-centimeter-long sections.

RADIOCARBON: Samples of 2-centimeter-thick intervals of sediment were taken from the cores. Data are reported at the midpoint depth of sampling intervals. The sediment samples were washed through stacked 450 micrometer, 150 micrometer, and 63 micrometer sieves to remove the less than 63 micrometer-sized sediment and to protect the finer sieves. The sediment remaining on the sieves was recombined, transferred to filter paper, left to air dry, and then placed in vials. The dried sediment was then spread out onto a picking tray and viewed under a microscope. Microscopic shells of mollusks, foraminifera, or plant/wood were removed with the aid of a picking brush or tweezers and placed into separate vials and weighed. These vials were then sent off for radiocarbon dating. Material was analyzed according to the NOSAMS Radiocarbon Method.

GEOPHYSICAL PARAMETERS (CORE LOGGER): A Geotek Multi-Sensor Core Logger (MSCL) running Geotek MSCL software was used to measure P-wave velocity, gamma ray density, and magnetic susceptibility. Logging was performed on unsplit sediment cores at the USGS PCMSC Core Lab at 1-centimeter intervals from the top of each 150-centimeter-long section of core. The reference core thickness was 9.373 centimeters. Data are reported at the bottom of sampling intervals. P-wave (primary wave) velocity was measured through the core with an acoustic rolling contact (ARC) transducer using a stationary active transducer element that couples directly to the core liner. Measurements were calibrated using a short length of liner filled with distilled water and comparison to a standard velocity of distilled water at a given temperature. P-wave velocity is given in meters per second. The P-wave travel time offset (PTO) was 20.9. Measurements below 1480 meters per second (typical speed in seawater) or missing data values were the result of poor coupling with the core liner or air voids in the core. Anomalous values for P-wave velocity were not excluded from the data. Bulk density based on gamma-ray attenuation was measured with a Cesium-137 gamma-ray source and gamma detector mounted on the MSCL. Gamma-ray density measurements were calibrated using an aluminum calibration piece mounted inside a water-filled polycarbonate core liner with width (W)=0.486 centimeters. Gamma-ray density calibration parameters were A=-0.0003 and B=-0.0550. Gamma-ray density measurements below 0.1 grams per cubic centimeter or missing data values were the result of poor contact with the core sample or air voids at the logging location. Anomalous values for gamma-ray density were not excluded from the data. A 120 mm-diameter Bartington MS2C loop was used to measure magnetic susceptibility on whole cores. The sensor is electronically calibrated with a supplied stable iron standard, and calibration parameters were A=1, B=0. Magnetic susceptibility measurements were collected every 1 centimeter with 5 second dwell times. Data are reported as corrected magnetic susceptibility in 10exp-8 SI dimensionless units.

SHORT-LIVED RADIONUCLIDE ACTIVITIES: 2-centimeter-thick intervals were subsampled from sediment cores for radionuclide determinations. Data are reported at the midpoint depth of sampling intervals. Prior to quantification by gamma spectrometry, bulk sediment was oven-dried at 60 degrees Celsius and ground to a homogeneous grain size. Short-lived radioisotopes were determined at the USGS Pacific Coastal and Marine Science Center (PCMSC) Radiochemistry Lab. Sediment packed into 10-milliliter polystyrene vials with air-tight caps and counted for 24 hours in a high-purity low-background germanium (HPGe) well detector. Unsupported Lead-210 activities were quantified by subtracting Lead-210 activities counted at the 46.52 keV peak from the average of supported Radium-226 activities counted indirectly at the Lead-214 351.9 keV peak and Bismuth-214 609.3 keV peak. Detector efficiencies for Lead-210 and Radium-226 were determined using IAEA standards RGU-1 and RGTh-1. Cesium-137 activities were counted at the 661.6 keV peak. Detector efficiency for Cesium-137 was determined using International Atomic Energy Agency (IAEA) Standard Reference Material 300.

TOTAL ORGANIC CARBON CONTENT (TOC): 2-centimeter-thick intervals were subsampled from sediment cores for TOC determinations. Data are reported at the midpoint depth of sampling intervals. TOC was calculated as the difference between total carbon and total inorganic carbon contents of bulk sediment which were determined coulometrically (UIC, Inc.) at the USGS Pacific Coastal and Marine Science Center Sediment Laboratory. Samples were run in duplicate. Average values are reported. Coulometer performance was verified relative to a calcium carbonate reference material.

ELEMENT CONTENTS: 2-centimeter-thick intervals were subsampled from sediment cores for elemental determinations. Data are reported at the midpoint depth of sampling intervals. Sediment was oven dried at 60 degrees Celsius, gently disaggregated, and dry-sieved in stainless steel sieves to obtain the less than 0.063 millimeter-diameter (fine fraction) of sediment. Fine sediment was sent to the USGS Analytical Chemistry Project, which subcontracted AGAT Laboratories, a nationally accredited laboratory, for determinations of elemental compositions. Sediment was decomposed by two methods: a near-total four-acid digestion with low limits of determination, ideal for elements present at trace (part per million) levels, and a total digestion by sodium peroxide fusion that targeted elements in refractory minerals such as chromium, zirconium, and rare earth elements. Quantification was performed by inductively coupled plasma optical emission spectroscopy (ICP-OES) for major elements and inductively coupled plasma mass spectroscopy (ICP-MS) for minor and trace elements. Total mercury was measured by cold vapor atomic absorption spectroscopy (CVAAS). Geologic reference materials, internal standards, and consistency standards were used for calibration, quality assurance, and quality control.